1. Field of the Invention
The present application relates generally to the field of write channel equalization in a magnetic recording device and in particular to a write equalization level control in a tape drive.
2. Description of the Related Art
Magnetic recording devices such as magnetic tape drives are used for recording computer data for storage and retrieval. Various techniques have been developed over the years to improve the characteristics of data reading and writing on magnetic media. One such development is write equalization recording.
In U.S. Pat. No. 5,255,130 is disclosed an adjustable write equalization for tape drives wherein a circuit and method are provided for adjusting write equalization pulses in a tape drive to achieve a desired suppression in the read signal.
U.S. Pat. No. 5,872,665 discloses a programmable write equalization for magnetic data recording wherein a circuit and a method for generating a write compensated write data signal for magnetic recording is provided. Extra write pulses are generated to adjust the pulse width and pulse spacing.
U.S. Pat. No. 5,339,202 discloses an adjustable write-equalized recording circuit for recording data on magnetic tape wherein the amplitude of write-equalisation pulse data waveform is varied by a preset amount or by a sensed amount.
In general, the effect of write equalization pulses can be controlled either by controlling the amplitude of the pulses or by controlling the width of the pulses.
Write equalization is generally used in tape drives in order to put some of the channel equalization on the write side, thereby reducing the amount required on the read side and improving the channel signal-to-noise ratio. Ideally, a write equalization circuit is a digital linear filter. However, the non-linear nature of magnetic recording processes make it desirable to control and adjust the pulses in order to achieve as linear a filter as is possible, given the magnetic non-linearities. Achieving a linear filter response is particularly important for partial response maximum likelihood (PRML) channels, requiring linear superposition of read pulses.
The high frequency nature of the write equalization generally leads to designing the media from the write driver circuit to the write head as a controlled impedance transmission line.